AbstractIn recent times, the employment of recycled aggregate concrete (RAC) for sustainable infrastructure development has enticed special interest from the research community owing to a greater emphasis on resource conservation and environmental protection. To apply such concrete in the modern-day construction industry, in-depth knowledge and thorough understanding of its fire resistance is imperative and an urgent need at the present time. Hence, this experimental study investigates the effect of elevated temperatures (25°C–800°C) on residual mechanical, physical, and microstructure performances of RAC strengthened via the coupling effect of chopped basalt fiber (BF) and pozzolana slurry treated recycled concrete aggregate (TRCA). To mimic real building fire conditions, concrete test specimens were heated to a specific target temperature in a controlled heating manner, and then their performance was assessed in terms of residual properties including compressive strength, splitting tensile strength, flexural strength, mass loss, physical appearance, and microstructure. Overall, the test findings revealed significant enhancement in residual properties of modified recycled concrete prepared by combined utilization of BF and TRCA. Moreover, in comparison with a reference sample, the BF-based recycled concrete demonstrated lower mass loss and surface degradation, especially beyond 400°C, that is attributed to the excellent thermal stability and reinforcing effect of BF. The microstructure observation evidenced improved matrix quality that contained better interfacial transition zones alongside added nucleation sites by BF. Lastly, based on the experimental data, simplified numerical relationships are established that will help predict the postfire performance of BF-reinforced sustainable concrete.